The man held over the disappearance of April Jones has now been arrested on suspicion of her murder, police have announced.
Mark Bridger, 46, who was initially arrested on suspicion of abducting the five-year-old, is being questioned by detectives.
The arrest "does not detract from our efforts to locate April and we remain committed to finding her", Detective Superintendent Reg Bevan said at a news conference earlier.
"Her family has been informed of this development and as you would expect they continue to be supported by a family liaison officer," he added.
Sky's Crime Correspondent Martin Brunt said: "Clearly it appears that the police are looking for a body now and have given up hope of finding April alive."
But one volunteer who has been helping in the search in mid Wales told Sky News: "If they haven't found her yet, there's a chance."
Specialist search teams endured a night of torrential rain and battled rough terrain as the investigation entered its fifth day. Officers are continuing to appeal to the public for any information they have ahead of a further news conference at 5.30pm.
Superintendent Ian John has acknowledged that volunteers had played a "vital part" in the hunt for April, who suffers from cerebral palsy.
But he said that given the nature of the search, officers were now insisting that only trained teams should be involved.
Officers have been focusing their search on a small stretch of the Dyfi River, which has risen a few feet after a night of heavy rain, and dog handlers are also involved.
A specialist sonar boat has been brought in to aid them, and Peter Faulding, an expert on confined spaces, is advising officers on the search at the river.
Mr Faulding gave evidence at the inquest of MI6 spy Gareth Williams , who was found dead in a locked holdall at his London flat in 2010.
Officials have now confirmed that Bridger attended the same school parents' evening as April Jones' mother and father just hours before she disappeared at about 7pm on Monday in Machynlleth.
She was reported to have willingly got into a vehicle after playing with friends near her home on the Bryn-y-Gog estate.
Bridger was seen at nearby Ysgol Gynradd Machynlleth, where two of his children are pupils. Witnesses saw the former leisure centre worker drive to the parents' evening, which started at 5pm, in his blue Land Rover Discovery - a vehicle for which police have issued an appeal for information.
Sources close to Mr and Mrs Jones said the couple had been given a "glowing report" about their daughter's progress - and had allowed her some extra play time when they returned home as a treat.
Police have been searching Bridger's three-bedroom cottage, out buildings, and garden in the hamlet of Ceinws.
Officers have also searched a guest house where Bridger is understood to have worked recently.
Police are appealing for anyone who saw Bridger or his blue Land Rover Discovery, registration number L503 MEP, in the hours between April's disappearance and his arrest at 3.30pm on Tuesday.
Because of the initial arrest, detectives have until 5pm today to charge or release him - but they are expected to apply for a further 24-hour warrant of detention.
April's family have launched a pink ribbon campaign to support the search. Her favourite colour is now tied in ribbons on gates and doorways in Machynlleth.
:: By Thursday evening police had received 2,500 calls following an appeal for information from the public. Anyone with information relating to the case is asked to call Child Rescue Alert Line on 0300 2000 333.
:: Machynlleth Town Council has set up an appeal fund for April and her family. To make a donation send a cheque payable to MTC-April's Fund, Y Plas, Aberystwyth Road, Machynlleth, Powys, SY20 8ER.